The present invention relates to a scroll compressor having a slider mechanism in the diametrical direction of an orbiting scroll.
FIG. 11 is a longitudinal sectional view of a conventional scroll compressor referred to in Japanese Patent Application No. 29127/1990 of the present inventors and FIG. 12 is a sectional view of the principal part thereof, illustrating the involvement of force acting on that part in operation. In FIG. 11, numeral 1 denotes a fixed scroll; 2, an orbiting scroll; 2a, a base plate; 2b, an orbiting bearing provided in the center of the counter-compression chamber side of the base plate 2a; 3, a frame secured by the fixed scroll 1 with bolts and the like; 4, an Oldham's ring for coupling the orbiting scroll 2 to the frame 3 in such a way as to make it revolve radially while preventing its rotation; and 5, a main shaft with an eccentric slider fitting shaft 6 formed in its upper end portion, the slider fitting shaft 6 having a flat surface 6a and a flat surface 6b in parallel to the axis of the main shaft 5. A slider 7 is fitted to the slider fitting shaft 6 so that it is slidable on the surface perpendicular to the axis of the main shaft 5 but prevented from rotating and that it is fitted in the orbiting bearing 2b in an eccentric state with respect to the axis of the main shaft 5. Numeral 8 denotes a hermetic container.
In FIG. 12, moreover, r represents the distance between the axis of the main shaft 5 (the center of the fixed scroll 1) and that of orbiting bearing 2b (the center of the orbiting scroll 2), that is, an amount of eccentricity; F.sub.C, the centrifugal force generated between the orbiting scroll 2 and the slider 7 while the orbiting scroll 2 is revolving; F.sub.g.theta., a compression load acting on the orbiting scroll 2 in the direction perpendicular to the centrifugal force F.sub.C ; F.sub.gr, a compression load acting on the orbiting scroll 2 in the direction opposite to the centrifugal force F.sub.C ; F.sub.n and .mu..sub.n respectively the contact force between the slider 7 and the flat surface 6a of the slider fitting shaft 6 and a friction coefficient therebetween, and F.sub.R, .mu..sub.R the contact force (pressing force) between the fixed scroll 1 and the orbiting scroll 2 in the eccentric and the counter-eccentric directions and a friction coefficient therebetween. Further, C represents the radial gap between the fixed scroll 1 and the orbiting scroll 2, and .theta. an angle in the slide direction of the slider 7 with the eccentric direction thereof, the slider 7 being inclined in the counter-rotational direction of the main shaft 5 with respect to the eccentric direction. Although the centrifugal force F.sub.C acts by nature on the center of gravity, and F.sub.g.theta. and F.sub.gr on the middle point between the axes of the main shaft 5 and orbiting bearing 2b, the moment resulting from the positional shifting of these forces is restrained by the Oldham's ring 4 and by preventing the repulsive force from being introduced from the Oldham's ring 4 into the system, it is assumed that these forces are totally acting on the axis of the orbiting bearing 2b, that is, the center of the slider 7. In FIG. 12, moreover, numeral 7a denotes a groove of the slider 7, 7b a contact flat surface of the slider 7, 7c a noncontact flat surface thereof, and 7d one end of the groove in the eccentric direction of the slider.
The operation will subsequently be described. When the main shaft 5 rotates, the orbiting scroll 2 revolves around the axis of the main shaft 5 while being guided by the Oldham's ring 4, whereby the compressive action is performed on the well known compression principle. During the steady operation, the slider 7 varies by the eccentric amount r determined by both scrolls in its slide direction, that is, up to the position where the orbiting scroll 2 contacts the fixed scroll 1 due to a component of the force in the slide direction of the resultant force of the centrifugal force F.sub.C and the compression loads F.sub.g.theta., F.sub.gr. Then the slider 7 presses the orbiting scroll 2 against the fixed scroll 1 and sets a radial gap C to 0 so that the compression action is initiated, the radial gap being provided between the eccentric and counter-eccentric directions of both scrolls. Moreover, the slider 7 is capable of sliding fore and back in the slide direction after it has slid by the eccentric amount r. Since both scrolls slide until they contact each other even when the shape of the spiral body between the fixed scroll 1 and the orbiting scroll 2 has shifted in a dimension, the radial gap C can always be set to zero during one revolution.
The force acting on the slider 7 and the orbiting scroll 2 includes, as shown in FIG. 12, the centrifugal force F.sub.C, the gas loads F.sub.g.theta., F.sub.gr, the contact force F.sub.R between the fixed scroll 1 and the orbiting scroll 2, and the frictional force .mu..sub.R F.sub.R resulting from the contact force F.sub.R, and the frictional force .mu..sub.n F.sub.n resulting from (the repulsive force of) the contact force F.sub.n between the slider 7 and the flat surface 6a. In FIG. 12, .mu..sub.n F.sub.n indicates the slide direction of the slider 7 in which the eccentric amount r increases because of the shifting (unevenness) of the shape of the spiral body. When the balance between the sliding direction of the slider 7 and the force perpendicular thereto is taken into consideration, the following expression may be introduced: EQU (F.sub.C -F.sub.gr -F.sub.R)cos.theta.+(F.sub.g.theta. +.mu..sub.R F.sub.R)sin.theta.=.mu..sub.R .mu..sub.n ( 1) EQU (F.sub.C -F.sub.gr -F.sub.R)sin.theta.-(F.sub.g.theta. +.mu..sub.R F.sub.R)cos.theta.=-F.sub.n ( 2)
When F.sub.n is eliminated from Eqs. (1) (2) and when the rest is subsequently solved for F.sub.R, the contact force F.sub.R between the fixed scroll 1 and the orbiting scroll 2 is expressed by EQU F.sub.R ={(F.sub.C -F.sub.gr)(cos.theta.+.mu..sub.n sin.theta.)+F.sub.g.theta. (sin.theta.-.mu..sub.n cos.theta.)}/{(.mu..sub.R .mu..sub.n +1)cos.theta.+(.mu..sub.n -.mu..sub.R)sin.theta.} (3)
With respect to Eq. (3), if the force acting on the slider 7 and the orbiting scroll 2 is simplified with .mu..sub.R =.mu..sub.n =0, the following model is assumed: EQU F.sub.R =(F.sub.C -F.sub.gr)+F.sub.g.theta. tan.theta. (4)
Since the mechanical properties of the scroll compressor are represented by F.sub.g.theta. &gt;&gt;F.sub.gr, the greater F.sub.g.theta., the greater F.sub.R becomes in the case of the slider mechanism as shown in Eq. (3) or (4).
Refrigeration or air-conditioning compressors often cause liquid compression in which a liquid refrigeration medium is directly compressed while the liquid refrigeration medium is still asleep in the compression chamber, that is, during so-called still-sleep starting, or while a large amount of liquid refrigeration medium is flowing into the suction pipe, that is, during liquid back operation. In this case, the pressure tends to leak from an outlet in the innermost compression chamber among a plurality of compression chambers constituting the scroll compressor and therefore the pressure is not increased conspicuously. However, the pressure is caused to increase noticeably in an intermediate or the outermost compression chamber unless there is provided a pressure escape therein. F.sub.g.theta. greatly increases in this state. Notwithstanding, F.sub.gr will not increase since it is the load determined by the difference between the exhaust and suction pressures and since the exhaust pressure is determined by the condensation temperature in view of the construction of such a scroll compressor. In the aforementioned conventional slider mechanism, while F.sub.R is growing at the time of liquid compression as shown by Eqs. (3), (4), that is, while the radial gap between both scrolls remains at zero at that time, the pressure in the intermediate or the outermost compression chamber (particularly in the intermediate pressure chamber) sharply increases because there is no escape therein. As a result, the increased pressure or F.sub.R that has sharply grown at the contact point between both scrolls may cause the spiral bodies of both scrolls to snap and break.
In another slider mechanism, it may be contrived to make the slide direction of the slider 7 conform to its eccentric direction. However, the contact force F.sub.R between the fixed scroll 1 and the rock scroll 2 is given by EQU F.sub.R =F.sub.C -F.sub.gr .+-..mu..sub.n F.sub.g.theta. ( 5)
since F.sub.n =F.sub.g.theta.. In this case, the sign denotes the occasion where the slider 7 slides in the direction in which the eccentric mount r increases because of the unevenness of the spiral sides of both scrolls in the lower case and conversely it slides in the direction in which the eccentric amount r decreases in the upper case. From Eq. (5), F.sub.R &lt;0 while the slider 7 is sliding in the direction in which the eccentric amount increases when F.sub.g.theta. sharply increases because of the liquid compression. Although the slider 7 tries moving back then, this means the slider 7 is to slide in the direction in which the eccentric amount decreases and therefore F.sub.R &gt;0 from Eq. (5). Ultimately, the slider 7 becomes stabilized in that state in view of the frictional force .mu..sub.n F.sub.g.theta. and there develops only an extremely small radial gap equivalent to the difference in the unevenness of the order of microns between the spiral body sides of both scrolls. The pressures in the intermediate and outermost compression chambers markedly increase because of the liquid compression and the gap of the order of microns is incapable of relieving the pressure. As a result, the pressure may cause the spiral bodies of both scrolls to snap and break.
In still another slider mechanism, unlike the aforementioned conventional one, it may be contrived to incline the slide direction of the slider 7 by .theta. toward its eccentric direction in the rotational direction of the main shaft 5. In this case, the contact force F.sub.R between the fixed scroll 1 and the orbiting scroll 2 is simplified by making reference to Eq. (4) and the following model is assumed: EQU F.sub.R =(F.sub.C -F.sub.gr)+F.sub.g.theta. tan.theta. (6)
In this method, however, F.sub.R &lt;0 as F.sub.g.theta. increases at the time of liquid compression, that is, the slider 7 moves back and produces a radial gap between both scrolls, thus allowing the pressures in the intermediate and outermost compression chambers to be relieved as pressure escapes are provided therein. During normal gas compression, however, the following condition must be met from Eq. (6): EQU F.sub.C &gt;F.sub.gr +F.sub.g.theta. tan.theta. (7)
to effect compression with the radial gap as zero, that is, to establish F.sub.R &gt;0. Notwithstanding, it is difficult to satisfy the condition of Eq. (7) with reference to every operating condition on the unit. There exists the operating condition under which the radial gap is produced between both scrolls as the slider 7 moves back when F.sub.R &lt;0 is established even at the time of gas compression.
When the slide direction of the slider is inclined toward its eccentric direction or toward the eccentric direction by .theta. in the counter-rotational direction of the main shaft in the slider mechanism of the conventional scroll compressor, the radial gap between both scrolls becomes as extremely small as what is in the order of microns or almost nearly zero at the time of liquid compression. As the pressure is not allowed to be relieved, the spiral bodies may be caused to snap because of the high pressure produced by the liquid compression. When the slide direction of the slider is inclined toward its eccentric direction by .theta. in the rotational direction of the main shaft, moreover, the radial gap is produced between both scrolls under such an operating condition that the condition of F.sub.C &gt;F.sub.gr +F.sub.g.theta. tan.theta. cannot be met during the normal gas compression and this poses a problem in that no compressive action is performed.